Add ability to inspect specific commits and diffs via command line arguments

**Is your feature request related to a problem? Please describe.**

It should be easily possible to inspect the changes by a given git commit/patch or range of commits.

**Describe the solution you'd like**

There should be command line arguments to show the git commits.

*Examples:*
```shell
# inspect a specific git commit
gitui --commit COMMITHASH

# inspect a range of commits
gitui --commit REV1..REV2

# inspect a range of commits and skip the first one
gitui --commit REV1^..REV2

# inspect from a given commit to HEAD
gitui --commit REV1..HEAD
gitui --commit REV1..

# inspect a git patch file
gitui --inspect SOMEFILENAME.patch
```

**Describe alternatives you've considered**

There should be a method via the CLI UI for selecting a range of commits or a patch file for inspection.

**Additional context**

- See [Git Revision](https://git-scm.com/docs/gitrevisions) on how a range of git commits can be specified
- See [Git Diff and Patch](https://www.freecodecamp.org/news/git-diff-and-patch/) and [Git Format-Patch](https://git-scm.com/docs/git-format-patch) on details of git patch files

Start by locating gitui's command-line argument parsing and the existing commit or diff inspection entry points. Review how the examples using --commit and --inspect should map to Git revision ranges and patch files. Done means the requested arguments work for the listed commit, range, HEAD, and patch-file cases.

Written by the indexing model from the issue text.